Submarine signaling appabatus



P 1945- B. M. HARRISON 2,384,465

SUBMARINE SIGNALING APPARA'IUS 5*. f I 7 9 a IO FmJ INVENTOR BERTRAM M.HARRISON FIG. 2

Patented Sept. 11, 1945 SUBMARINE SIGNALING APPARATUS Bertram M.Harrison, Newton Highlands, Masa, asslgnor to Submarine Signal Company,Boston, Mass., a corporation of Maine Application January 19, 1938,Serial No. 185,751 Renewed June 22,- 1939 14 Claims.

The present invention relates to a submarine signaling device and moreparticularly to a device for transmitting and receiving compressionalwaves under water.

An object of the present invention is to provide an improvedcompressional wave sendin and receiving device. A further object of thepresent invention is to provide such a device employing piezo-electriccrystals. A further object of the present invention is to provide acompressional wave sending and receiving device particularly suitablefor small echo sounding systerm.

A form of the present invention is shown in the accompanying drawing inwhich Fig. 1 is a mid-sectional elevation and Fig. 2 is across-sectional plan view taken along the line II-II of Fig. 1.

As shown in the drawing the device is housed within a casing formed of ashell I having an external flange 2. The shell I is adapted to besecured within an aperture in the hull 3 of a vessel by means of aclamping ring 4 which is threaded on the outside of the shell I as shownand together with the flange 2 holds the unit firmly against th hull.Acoustic insulating material 5, such as rubber, is preferably insertedbetween the signaling unit and the ships skin.

The lower end of the shell which is in contact with the outer water isclosed by a diaphragm 6 having special characteristics to be describedlater. The diaphragm is held in place in the shell I between an innerflanged ring I abutting a shoulder 8 in the inside of the shell and anouter flanged ring 9 pressed against the diaphragm by the threaded ringI0 engaging internal threads in the shell I.

The upper or inner end of the shell I is closed by a cylindrical cap IIthreaded into the shell I. The cap H is firmly screwed down so that theshoulder I2 on the cap abuts th end of the shell I, a rubber gasket I3being interposed between these two elements.

The active member of the signaling device is mounted entirely within thecap II. An inwardly extending fiange I! will be noted in the upperportion of the cap. To this flange is fastened a plate I8 by means ofthe screws I'l. Secured to'the plate I6 is a cylindrical mass member I.having its lower end hollowed out so that it terminates in a cylindricalshell l9. Within this shell l9 are mounted piezo-electric crystals 20,for example of Rochelle salts, in such amanner as to make them as rigidand as nearly a part of the mass l8 as possible.

To this end the interior of the hollowed-out portion of the mass I8 islined with insulating material such as a thin Bakelite disc 2I and athin cylindrical strip 22. A group of crystals 20 ar cemented by theirends against the member 2| which is cemented to the member I9. Thecrystals are firmly held against sidewise motion by slightlywedge-shaped pieces 23 of insulating material which fit firmly againstth insulating strip 22 within the shell I8 and the crystals. In order tomake the assembly still more rigid, the insulating blocks'23 are screwedto the shell I9 by means of the screws 24. The crystals 20 have theirfiat faces coated with metal foil as electrodes and are separated fromeach other'by thin metallic strips 25 placed between adjacent crystalswithin those portions thereof which are within the shell l9. Thus, thelower ends of the crystals are free from contact with each other andwith any solid element of the unit. Within the shell I9, however, thecrystals and metallic strips are firmly clamped together whereby thecrystals are rigidly fixed to the mass I8. The metallic strips 25 serveto connect adjacent crystals in series electrically. Electricalconnection to the group of crystals is made to the external electrode ofeach of the end crystals of the group by means of the leads 26 and 21which are brought upward through apertures in the insulating wedges 23,the mass element IS, the plate I6 and the upper end of the cap II. Inpassing through the cap the leads 26 and 21 are preferably Joined into acable 28 which is made watertight with the cap II by means of suitablepacking 29 and the clamping nut 30.

The interior of the signaling device is filled with a suitablesound-conducting medium, such as oil, through the filling aperture nearthe top of the cap II which may be closed by the plug 3|.

Considering, now,. the acoustical features of the device according tothe invention, it has already been mentioned that the piezoelectriccrystals 20 are firmly fixed to the mass I8. The latter is made largeenough so that it will act as a substantially infinite mass. The optimumheight of the element I8 measured in the vertical direction, as shown inFig. l, is one-eighth of the wave length of the compressional waveswithin the material of which it is made at the signaling frequency orone-eighth plus any multiple of one-half wave length. Since the mass itis substantially infinite in effect, it will remain stationary and theportions of the crystals adjacent the mass will have zero amplitude ofvibration while the lower ends of the crystals near the diaphragm 8 willhave maximum amplitudes of vibration.

The velocity of the free end of the crystals 20 at signaling frequenciesof 10,000 cycles per second or over is too high to make it possible toobtain efllcient transfer of power to the water directly. For thisreason an impedance-matching transformer is required between the crystaland the water.

The crystal 20 is made one-quarter wave length long below the clampingline and, as has been mentioned, the element It is made oneeighth of awave length long in order that it may have maximum mass reactance. Thespace between the crystal and the diaphragm 6 is made less thanone-quarter wave length thick in order that no standing waves shall bepresent. The diaphragm 6 is made substantially one-quarter wave lengthin thickness in order to provide optimum impedance and loading on thecrystal to transfer maximum energy from the crystal to the water.Moreover, the material of the diaphragm shoul preferably be chosen tohave at one-quarter wave length thickness an impedance which issubstantially the geometric mean between the crystal impedance and thewater impedance.

Where the crystal is of Rochelle salt, I have found to be particularlywell suited for the diaphragm material one of the phenolic condensationproducts, and especially a substance known under the trade name ofSynthane Grade C. This substance has a specific gravity of about 1.35and the velocity of compressional waves therein is about 9000 feet persecond. In the arrangement described I have found that sufllcient poweroutput and sensitivity as a receiver can be obtained to make a highlyefficient depth sounding system particularly for the measurement ofrelatively shallow depths when signaling frequencies of 10,000 cyclesper second or over are employed.

Having now described my invention, I claim:

1. A submarine compressional wave sender and receiver comprising ahousing open at one end, a mass element supported therein, apiezo-electric crystal having a longitudinal dimension and bein rigidlyfixed by one end to said mass element and a diaphragm closing the openend of the housing and positioned with its inner surface close to thefree end of sai crystal, said mass element having a longitudinaldimension parallel to the iongitudinal dimension of the crystal andsubstantially equal to one eighth, the free portion of the crystalhaving a longitudinal dimension of one fourth and said diaphragm havinga thickness of one fourth, all said dimensions being in fractions of awave length of compressional waves of the signaling frequency in therespective materials.

2. A submarine compressional wave sender and receiver comprising ahousing open at one end, a mass element supporte therein, apiezo-electric crystal having a longitudinal dimension and being rigidlyfixed by one end to said mass element, a

diaphragm closing the open end of the housing and positioned with itsinner surface close to the free end of said crystal, said mass elementhaving a longitudinal dimension parallel to the lonitudinal dimension ofthe crystal and substantially equal to one eighth the free portion ofthe crystal having a longitudinal dimension of one fourth and saiddiaphragm having a thickness of one fourth, all said dimensions being infractions of a wave length of compressional waves of the signalingfrequency in the respective materials, and a compressional waveconducting liquid filling the space within the housing between thecrystal and the diaphragm.

8. A submarine compressional wave sender and receiver comprising ahousing open at one end, a mass element supported therein, a Rochellesalt piezoelectric crystal firmly fixed by one end to said mass element,a diaphragm closing the open end of the housing and positioned with itsinner surface close to the free end of said crystal. said diaphragmbeing composed of a phenolic condensation product and having a thicknessof substantially one quarter of a wavelength of compressional waves ofthe signaling frequency in the diaphragm material, and a liquid,compressional wave conducting medium within the casing filling the spacebetween the free end of the crystal and the diaphragm.

4. A submarine compressional wave sender and receiver comprising ahousing open at one end, a mass element supported therein, a Rochellesalt piezoelectric crystal firmly fixed by one end to said mass element,a diaphragm closing the open end of the housing and positioned with itsinner surface close to the free end of said crystal, said diaphragmbeing composed of Synthane and having a thickness of substantially onequarter of a wavelength of compressional waves of the signalingfrequency in the diaphragm material, and a liquid, compressional waveconducting medium within the casing filling the space between the freeend of the crystal and the diaphragm.

5. A submarine compressional wave sender and receiver comprising ahousing open at one end, a mass element supported therein, a Rochellesalt piezoelectric crystal firmly fixed by one endto said mass element,a diaphragm closing the open end of the housing and positioned with itsinner surface close to the free end of said crystal, said diaphragmhaving a. thickness of substantially one quarter of a wavelength ofcompressional waves of the signaling frequency in the diaphragm materialand having an acoustical impedance which is substantially the geometricmean between the crystal and the water impedances, and a compressionalwave conducting liquid within the casing filling the space between thefree end of the crystal and the diaphragm.

6. A submarine compressional wave sender and receiver comprising an openended cylindrical housing, adapted to be mounted in an aperture in thehull of a ship, a diaphragm of a phenolic condensation material closingthe outer end of the housing and having a thickness of one quarter of awave length of compressional waves of the signaling frequency in thediaphragm material, a cup-shaped cap closing the inner end of thehousing, a metallic mass element having a thickness of one-eighth of awave length secured within said cap, a plurality of piezoelectriccrystals firmly secured to said mass element and having a free portion aquarter wave length long, and a compressional wave conducting liquidsubstantially filling all residual spaces within said housing.

7. A submarine compressional wave sender and receiver comprising ahollow cylindrical shell open at both ends adapted to be mounted in anaperture in the hull of a ship, a diaphragm closing the outer end of theshell, said shell having a threaded portion adjacent its inner end, acup-shaped cap having a threaded portion adapted to engage said threadedportion of said shell and thereby to close the latter, and a pluralityof piezoelectric crystals mounted within said cap, whereby the cap canbe removed from the interior of the ship for inspection and replacementof the crystals.

8. A submarine compressional wave sender and receiver comprising ahollow cylindrical housing closed at one end by a compressional waveconducting diaphragm and at the other end by a cap member havingconcentrically mounted therein a cylindrical mass member ter- I minatingat the end facing the diaphragm in a cup, a group of rectangularprismoidal piezoelectric crystals mounted in said cup with vibra-'tional axes parallel to the axis of said mass member and means forfirmly holding said crystals in said cup including a plurality of wedgesof insulating material shaped to fit tightly between the rim of the cupand the crystals.

9. A submarine compressional wave sender and receiver comprising ahollow cylindrical housing open at one end, a compressional waveconducting diaphragm having a thickness of substantially a quarter wavelength at the signaling frequency closing the open end of the housing, aquarter wave length vibratory piezoelectric crystal means loaded at oneend by an effectively infinite mass member, means including said massmember for securing said crystal means within said housing with the freeend of the crystal means in proximity to said diaphragm and acompressional wave conducting liquid filling the space between thecrystal means and the diaphragm.

10. A submarine compressional wave sender and receiver comprising ahollow cylindrical housing open at one end, a compressional waveconducting diaphragm of a phenolic condensation material having athickness of substantially a quarter wave length at the signalingfrequency closing the open end of the housing, a quarter wave lengthvibratory piezoelectric crystal means loaded at one end by aneffectively infinite mass member, means including said mass member forsecuring said crystal means within said housing with the free end of thecrystal means in proximity to said diaphragm and a compressional waveconducting liquid filling the space between the crystal means and thediaphragm.

11. A submarine compressional wave sender and receiver comprising ahollow cylindrical housing open at one end, a compressional waveconducting diaphragm having a thickness of substantially one-quarterwave length as measured in the material at the signaling frequency, saiddiaphragm closing the open end of the housing, a longitudinallyvibratable element having a length substantially equal to one-quarterwave length as measured in its material at the signaling frequency, saidelement being loaded at one end by a mass member having a lengthsubstantially equal to one-eighth wave length as measured in itsmaterial at the signaling frequency, means including said mass memberfor securing said vibratable element within said housing with the freeend of the element in proximity with said diaphragm and a compressionalwave conducting liquid filling the space between the vibratable elementand the diaphragm.

12. A submarine compressional wave sender and receiver comprising ahousing open at one end, a mass element supported therein, alongitudinally vibratable element firmly fixed by one end to said masselement, a diaphragm closing the open end of the housing and positionedwith its inner surface close to the free end of said vibratable element,said diaphragm having a thickness of substantially one quarter of a.Wave length of compressional waves of the signaling frequency in thediaphragm material and having an acoustical impedance which issubstantially the geometric mean between the impedance of the vibratableelement and the water impedance and a compressional wave conductingliquid within the casing filling the space between the free end of thevibratable element and the diaphragm.

13. An acoustical apparatus comprising in combination a housing open atone end, a diaphragm closing the open end, a mass element entirelysupported in and by said housing, electromechanical energy interchangingmeans including means firmly fixing the same at one end to said masselement and having its other end free in juxtaposed relation withrespect to said diaphragm.

14. A closure for use with an acoustical apparatus comprising incombination a cap member having attached thereto a mass element havingsecurely fixed at one end and thereby supporting an electromechanicalenergy interchanging means and said electromechanical energyinterchanging means having a free end acoustically coupled to avibration propagating medium.

BERTRAM M. HARRISON.

